The use of flaps to divert normally axially flowing exhaust gases from a propulsion gas turbine engine in an aircraft application is well known. Such flaps are typically pivoted or otherwise positioned to selectably divert at least a portion of the exhaust gases to provide thrust vectoring for increased maneuverability and/or lift.
As with any aircraft related component, such vectoring exhaust nozzles and flaps are desirably designed to be relatively light in weight as compared to non-aircraft structures subject to similar pressure or stress loading.
For simply supported flaps having a spanwise orientation transverse to the exhaust gas stream, the gas static pressure at the flap surface results in a large bending moment at the flap midspan which is hence the point of maximum flap deflection.
In modern, high performance nozzles wherein the gas static pressure loading and mechanical complexity are increased over prior art nozzle designs, it is not uncommon to have a diverting flap which, although adequate in material strength to withstand the gas dynamic and static forces during nozzle operation, is elastically deflected by such forces to a degree which results in interference between the moving flap and surrounding nozzle components. Such flap designs must be modified to reduce the midspan deflection by increasing the cross span moment of inertia and hence the weight and/or cross sectional thickness of the flap. Modifications of this type result in an even further understressed flap design which is heavier and bulkier than desired for optimum performance.